Hydroacoustic transducer with centering means



Sept. 27, 1966 J. v. BoUYoUcos HYDROACOUSTIC TRANSDUCER WITH CENTERING MEANS 8 Sheets-Sheet l Original Filed Nov. lO

D40.. OF

INVENTOR JOHN V. BOUYOUCOS BW //n-a/ A7' TORNEY Sept 27, 1966 J.. v. BoUYoUcos HYDROACOUSTIC TRANSDUCER WITH CENTERING MEANS 8 Sheets-Sheet E Original Filed Nov. lO, 1961 ATTUR/VEY Sept. 27, 1966 HYDRoAooUsTIc TRANSDUCER Original Filed Nov. l0, 1961 J. V. BOUYOUCOS WITH CENTERING MEANS 8 Sheets-Sheet 5 i l:um

JOHN V.

1N TOR.

UYOUCOS ATTORNEY Sept- 27, 1966 .L v. BoUYoucos 3,275,977

HYDROACOUSTIC TRANSDUCER WITH CENTERING MEANS Original Filed NOV. 10. 1961 8 Sheets-Sheet 4 VENTOR. ./0 V. 50u rol/C05 ATTORNEY Sept. 27, 1966 J.. V, BQUYOUCOS 3,275,977

HYDROACOUSTIC TRANSDUCER WITH CENTERING MEANS Original Filed Nov. lO, 1961 8 Sheets-Sheet 5 N iw f INVENTOR. JoH/v v. Bow/00005 Sept. 27, 1966 J.v. BOUYOUCOS 3,275,977

HYDROACOUSTIC TRANSDUCER WITH CENTERING MEANS 8 Sheets-Sheet 6 Original Filed Nov. l0, 1961 Sept. 27, 1966 .1.4 v. BoUYoucos 3,275,977'

HYDROACOUSTIC TRANSDUCER WITH CENTERING MEANS 8 Sheets-Sheet 'I Original Filed Nov. lO, 1961 INVENTOR. JOHN V. Boum/C05 BWL TTOR/VE Y Sept. 27, 1966 Jqv. BoUYoucos 3,275,977

RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR NS l 8 Sheets-Sheet 8 United States Patent O 3,275,977 HYDROACOUSTIC TRANSDUCER WITH CENTERING MEANS John V. Bouyoucos, Blossom Circle E., Rochester, N.Y.

Original application Nov. 10, 1961, Ser. No. 151,516, now Patent No. 3,212,473. Divided and this application May 28, 1965, Ser. No. 459,859

9 Claims. (Cl. 340-15) The present invention relates to hydroacoustic 'apparatus and particularly to hydraulic centering, such apparatus having improved hydraulic centering means. This application is a division of my copending patent application, Serial Number 151,516, now Patent No. 3,212,473, tiled November 10, 1961, for Electro-Hydroacoustic Transducer.

In the said copending patent application there is described an electro-hydroacoustic transducer for generating acoustic energy of a relatively broad frequency band from the flow of hydraulic fluid under pressure. The electro-hydroacoustic transducer is characteristic in that a high level of acoustic energy can be generated in response to a low level electrical control signal.

Acoustic energy is generated by the hydroacoustic transducer by modulating an otherwise steady flow of fluid by a ow modulating means including a valving element. The modulating process produces an acoustic energy which may be cou-pled directly to an acoustic load or may be used to drive one or more subsequent valve stages of larger displacement, thereby providing power amplification.

As is more fully pointed out hereinafter, there are serious mechanical problems involved in the subsequent or driven valve stages, particularly when springs are used for establishing and maintaining an equilibrium position of a valve in the subsequent stage. Mechanical means, such as springs, may fatigue and fail under repeated stroking of the valve in the subsequent valve stage.

Accordingly, an object of the present invention is to provide a hydraulic centering means for establishing and maintaining an equilibrium position of the valving element.

A further object is to provide an improved hydroacoustic apparatus having hydraulic centering means for a power valve in a driven or subsequent stage of hydroacoustic apparatus which may be repeatedly stroked without failure due to fatigue.

It is still another object of the present invention to provide an improved hydraulic centering means for centering a power valve of multi-stage hydroacoustic apparatus, in spite of dynamic actuation of the valve which cyclically displaces the valve to opposite sides of its centered position.

Other objects, features and advantages of this invention will become apparent from the description, taken in conjunction with the drawings wherein:

FIG. 1 is a block diagram showing schematically the principle of operation of the electro-hydroacoustic transducer according to the invention;

FIG. 1A is a fragmentary diagram showing a modification of the electro-hydroacoustic transducer system shown in FIG. 1;

FIG. 2 is a central cross-sectional view of an electrohydroacoustic transducer employing push-pull flow modulation and push-pull drive of the power output coupling means;

FIG. 3 is a central cross-sectional view of a transducer embodying a push-pull valve amplifier driving a singleended radiating structure;

FIG. 4 is a central cross-sectional view showing a trans- 3,275,977 Patented Sept. 27, 1966 ducer embodying a push-pull valve lamplifier driving a double-ended radiating assembly in push-pull;

FIG. 5 illustrates in central cross-section a transducer wherein single-ended valving is employed to drive a radiating means in push-pull;

FIG. 6 is a central cross-sectional view of a transducer incorporating single-ended valving and single-ended drive;

FIG. 7 discloses a transducer in central cross-section which differs essentially from that of FIG. 6 in that two radiating means are driven in push-pull;

FIG. 8 illustrates a. transducer in cross-section having two valving stages;

FIG. 9 discloses a device in cross-section incorporating push-pull modulation and single-ended coupling means wherein the modulation occurs on both halves of the cycle in the drive cavity associated with the coupling means; and

FIG. l0 illustrates in central cross-section a two-stage device incorporating means for maintaining the power stage statically in its null position.

Referring to FIG. l of the drawing, a schematic diagram of an electro-hydroacoustic transducer is shown wherein energy in the form of a fluid owing under pressure is converted into acoustic energy which may be delivered to a suitable acoustic load. This conversion of unidirectional flow energy to acoustic energy is accomplished by means of a flow switching or modulating element 12 interposed in the path of a fiowing fluid which is set in motion within a closed hydraulic system by a pump 15. The timing and magnitude of the switching action is determined by an electrical control input signal which may feed an electromechanical exciter 14; the latter actuates the flow switching device. The mechanical link between the exciter 14 and the ow switch 12 is indicated by a dashed line.

Interrupted pulses of flow energy, as generated by the switching element 12, are supplied to a resonant acoustic tank circuit 16. A portion of the acoustic energy is stored in the tank circuit, while a further portion may be transferred through a load coupling circuit 18 to a terminal load.

In some instances, as shown in FIG. 1A, the fluid pump may be connected between different portions of the switching element 12 through acoustic low-pass filters 13a and 13b, which isolate the acoustic circuit from the unidirectional fluid ow circuit. In the system of FIG. 1, however, the uid flows through a portion of the acoustic tank circuit; in this case, the uid is introduced into the acoustic tank circuit at a region Where there is zero pressure variation, so that the acoustic portion of the system is isolated from the hydraulic system.

FIG. 2 illustrates one embodiment of an electro-hydroacoustic transducer according to the invention. The transducer 10 of FIG. 2 consists of a movable piston assembly 20 which includes a piston radiator 21 forming one end of a stationary housing 23; the housing 23 contains the structure which performs the hydroacoustic amplification.

The piston radiator 21, also referred to simply as the piston, forms an extension of the shaft 24 of piston assembly 20 and is free to move as a rigid body axially with respect to cylindrical bore 26 in consequence of acoustic pressure signals generated in drive cavities 31 and 32 and acting in push-pull on drive flange 28 of metrical branches 48 and 49 to enter respective cavities 31 and 32. vThe direction of fluid flow through the housing 23 is indicated in FIG. 2 and the various figureslof the drawing by arrows. The branches 48 and 49 comblne to form a loop 50 whose function will be described more fully subsequently. From cavities 31 and 32 the liuid passes through ports S2 and 53 to respective orifices l34 and 35 from whence theiiow exits at reduced pressure into a discharge chamber 55. The latter may -be integral with an outlet line 56 communicating with exit 57. Seals 36 prevent leakage of fiuid from drive cavities 31 and 32 into the larger cavities 26 and 65. Accordingly, the loop 50 and the various chamber orifices provide a path for the flow of fluid under pressure through the housing.

Valve 40 may be driven axially past stationary port structure 45 by means of an electromechanical force generator 14 which may include a moving coil 58 free to move in magnetic gap 59 when energized by an electrical control input signal supplied to coil 58 through a leadin assembly 60. The exciter coil 58 is wound on a portion of a spider 62. The movement of coil 58 is communicated to valve 40 through a connecting rod 63. If the resonant frequency defined by the mass of the moving system and the stiffness of the spider is placed above the operating frequency range of the transducer 16, the displacement of valve 40 will lbe directly proportional to, .and in phase with, the input cu-rrent. In moving in reciprocal fashion within the bore of 64, valve 40 can open orifices 34 and 35 alternately.

The equilibrium position of valve 40 may be such as to create a zero lap condition between rims 37 and 41 and between rims 38 and 42. If the valve 40 is displaced to the right from equilibrium posit-ion, the right-hand orifice 34 is opened while the left-hand orifice remains closed. On the other hand, if valve 40 is displaced to the left from its equilibrium position, the left-hand orifice 35 opens while right-hand orifice 34 remains closed. Thus, for a sinusoidal input to the exciter, either orifice can be opened for approximately 50% of an oscillation period of the valve and a class B mode of modulation is obtained.

Although class B operation is achieved with zero lap at each orifice `between the associated metering rim of the valve and the corresponding rim of the port structure, class A operation may be achieved if the metering rims 37 and'38 of valve 40, at equilibrium, underlap respective rims 41 and 42 of the inwardly extending portions 43 and 44 of the port structure 45. In other words, orifices 34 and 35 will be open at both extremities of the valve movement and fluid will flow at all times through both of the orifices 34 and 35. Similarly, if the equilibrium position of valve 40 is biased to an overlap condition relative to the rims of the port structure 45, then each orifice will be closed at equilibrium and will be opened during one cyclical departure from equilibrium. Each orifice then will be open only during a minor portion of each cyclical excursion of the valve. This represents class C operation.

Since all of the orifices offer a resistance to the flow of uid which varies with displacement of the valve 40, each orifice 34 and 35 can be considered as a variable resistance. The asymmetrical modulation of fiow through oriiices 34 and 35 can be represented practically in terms of volume velocity sources which inject acoustic volume velocity alternately through ports 52 and 53 into cavities 31 and 32, respectively. Considering the impedance presented to the upstream side of the orifices, the acoustic compliance of cavities 31 and 32 is found to be in parallel with the inertance of feed line loop 50. The parallel relationship results since a variational velocity disturbance generated by an area change at the orifices can give -rise either to compression or expansion of the fluid within cavities 31 and 32, or to motion of uid in loop 50. The combination of cavities 31 and 32 and loop 5t) thus constitutes the acoustic tank circuit 16 of FIG. 1. As the pressure variations in cavity 32 are 180 degrees out of phase with the pressure variations in cavity 31, somewhere between cavities 31 and 32 at the nominal operating frequency one expects to find a point of zero pressure variation in feed line 5l). This point is used as the feedin point for hydraulic fiuid, thereby reducing the possibility of coupling energy from the acoustic tank circuit of the transducer back into the unidirectional fiow source.

Variational volume velocity injection from orifices 34 and 35 into the parallel tank circuit will result in pressure variations therein which, in turn, operates on the drive surfaces of the liange 2S of piston assembly 20 to generate motion of the piston 21 against an external load. The piston radiator 21 is shown backed by cavity 65 filled with a compliant liuid; the compliance of the fluid filled cavity should be such as toy resonate with the mass of the combined piston assembly at the design center or nominal operating frequency by which is meant the mean operating frequency of the control signal. As long as piston 21 moves essentially as a rigid body with respect to the compliant fluid in cavity 65, the load coupling circuit is a series resonant circuit, since the compliant liuid must always assume the same velocity as the piston.

The series load coupling circuit should be in resonance at the nominal operating frequency for optimum power transfer from the acoustic tank circuit to the load. In addition, the parallel acoustic tank'circuit should simultaneously be in resonance at the nominal operating frequency to enable the orifices to encounter a resistive load. Without the inertance of loop 50, the simultaneous satisfaction of both resonance conditions obviously would be impossible. Because of the presence of the inertance formed by loop 50, however, it is possible to tune the acoustic tank circuit and the load coupling circuit to resonance independently. The yacoustic circuit of the transducer thus takes the form of -a parallel tuned resonant circuit in combination with a series load coupling circuit and is effectively anfL-section bandpass filter.

One advantage of the bandpass filter is that a condition of maximum -power transfer to the load is assured, since, at the design center or nominal operating frequency, both the parallel acoustic tank circuit 16 and the series load coupling circuit 18 may be simultaneously atresonance.

Another advantage of such a composite circuit configuration is that, for a given 0 of the series branch, a broader bandwidth may be obtained than will be the case in the absence of the parallel resonant tank circuit. Accordingly, the frequency range of the transducer 10 and control signals can be broader. Furthermore, the phase angle of the driving point impedance, as seen from the amplifier orifices, will remain nearly resistive over the major portion of the passband. This characteristic of a constant-k filter is particularly useful since the power conversion efficiency of the drive amplifier can remain high over the passband.

The presence of loop 50 further acts as a short circuit between drive cavities 31 and 32 at zero frequency and prevents thrust being built up across the lopposite drive areas of the drive flange 28 of piston 21, thereby enabling piston 21 to exhibit inherent static stability. In other words, loop 50 `acts as an inlet for the operative fluid, as a short circuit at zero frequency across the drive fiange 28 of piston assembly 20, and as an important acoustic circuit element in the bandpass filter configuration. Loop 50, furthermore, enables the flow inlet to occur at a null or zero pressure variation point in the acoustic system, thereby minimizing the transfer of acoustic energy back into the hydraulic system.'

The transducer of FIG. 2 further includes a loop 66 which is intended to present an acoustic short circuit between opposing ends of valve 4f) to minimize the driving impedance of said valve. A barrier 70 which may be of flexible material, such as rubber, is transparent acoustically;V this barrier separates the externall fiuidwhich may be sea water-from the fluid in backing cavity 65, which may be the same hydraulic fluid used to operate the transducer. The gap 69 between the piston 21 and the housing 23 allows the static pressure to be the same on bot-h sides of piston assembly 20, thereby allowing the latter to be balanced statically. If, for example, the transducer of FIG. 2 is to be operated beneath the surface 'of the sea, the -piston assembly can be pressure equalized at any submergence depth to the external pressure through barrier 70. However, the

acoustic impedance of gap 69 is intended to be high compared either with the compliant reactance of cavity 65 or with the acoustic radiation impedance presented to radiator 21. In addition, if the uid in gap 69 is mass controlled, and if the resonant frequency defined by the mass of the uid in the gap acting with the stiffness of the fluid in cavity 65 is below the operating frequency, then the motion of the uid in the gap will be in phase with the piston motion. Under these circumstances, the gap functions somewhat in the manner of the port of a bass reex loudspeaker.

If the iiuid in cavity 65 is chosen to be identical with the hydraulic circuit fluid, the seals 36 may be removed, allowing a small leakage flow continuously into cavity 65. In these circumstances, cavity 65 must have a return connection to the reservoir so that static pressures do not build up therein.

FIG. 3 is a view of a modification of the device of FIG. 2 in which push-pull iiow modulation or switching of uid ow is achieved, as in FIG. 2, but wherein a single-ended power output coupling device is employed, in contrast to the push-pull drive of the power output coupling piston in the device of FIG. 2.

In this ligure, and in the remaining figures of the drawings, corresponding elements will be indicated by the same reference numeral as in FIG. 2. In those instances wherein the element is substanti-ally equivalent to but of somewhat diterent construction than, the element of FIG. 2, such element will be designated by a reference numeral `differing from that in FIG. 2 by some multiple of 100.

The transducer 10 of FIG. 3 is contained within a housing 123 into which hydraulic fluid is introduced under pressure at inlet 47 and from which the uid exhaust is at reduced pressure at outlet 56. Terminating at one end of the housing is a massive radiating piston assembly 120 having a mass which may resonate as a rigid body with a total mechanical stiffness of a plurality of springs 72 at the center frequency of operation. The springs 72 will replace the compliance presented by the liquid contained in cavity 65 of FIG. 2. In contrast to the device of FIG. 2, wherein the net static thrust on the piston assembly is zero, an average thrust is exerted on the piston of FIG. 3 owing to its exposure to the high pressure present in cavity or chamber 131. Bias against this net thrust is supplied by the springs 72. The dynamic force driving the radiating member 121 is derived from'l acoustic pressure signals in acoustic cavity 131 which a-ct on the exposed driving surface 75 of the coupling assembly 120 and which are generated by the valve 40. Seals 71 are provided in peripheral grooves in piston radiator 121 to prevent leakage of hydraulicfluid past the space between piston radiator 121 and the housing 123. The valve originates the required drive pressure signals by modulating the ow of fluid through acoustic cavities or chambers 131 and 132 in response to a control electrical signal input, not shown in FIG. 3 since it may be brought out of the housing 123 in a plane perpendicular to the paper. The spool type valve is free to move back and forth in response to a force applied by the electromechanical device 14 through connecting rod 63. The hydraulic circuit or fluid path of the transducer may be traced from inlet 47 to the mid-point of loop S0, through acoustic cavities 131 and 132 and thence to annular oriiices 34 and 35 formed, respectively, between the circular metering rim 37 of valve 40 and corresponding metering rim 41 of stator port structure 45 and between metering rim 38 of valve 40 and metering rim 42 of stator port 45. The flow then enters discharge cavity on the way to exit 57.

If, as shown in FIG. 3, the valve is normally in a zero lap condition at both orifices 34 and 35 so that, for no input current, metering rim 37 of valve 40 is in line with metering rirn 41 and metering rim 38 is in line with rim 42, a displacement Vof valve 40 to the right will cause a proportional opening of orifice 34, while orifice 35 remains closed; similarly, a displacement of valve 40 to theleft results in orifice 35 opening and orifice 34 remains closed. For a sinusoidal input, therefore, each of the orifices 34 and 35 is thus open for 50% of the signal period and class B operation is attained. It is evident that, as in the case of FIG. 2, class A or class C amplification can be achieved by appropriate biasing of the equilibrium position of valve 40 to an underlap condition or an overlap condition, respectively, relative to stator port 45.

The transducer of FIG. 3, whi-le embodying 'a push-pull amplifier, drives a single-ended load coupling circuit which may be identified as the resonant piston spring assembly 121, 72. The acoustic tank circuit of the transducer of FIG. 3 may be considered to comprise the cornlbination of cavities 131 and 132 and `loop 50. The acoustic tank circuit is terminated in a radiation impedance whose parameters may be frequency dependent. The acoustic tank circuit is driven by a source having characteristics of a variable resistance Ior modulating element and this circuit is shunt fed unidirectional energy through the feed line inertance of loop 50 from the constant pressure hydraulic supply, which is analogous to an electrical battery.

Since the device of FIG. 3 is a push-pull amplifier, that is a device utilizing push-pull switching, cavities 131 and 132 have been made equal in size to accommodate pushpull flow modulation and both cavities are ported by valve 40 at orifices 34 and 35 on alternate halves of the modulation cycle. Because of the symmetry of the tank circuit of the device of FIG. 3, the hydraulic inlet line 47 may bisect the feed line 50. For the same area of piston exposed to the drive cavity or cavities, the driving force exerted on the piston in the device of FIG. 3 ils one-half that for the device of FIG. 2. This condition results from the fact that acoustic for-ces are exerted on both faces of flange 28 of the piston of FIG. 2 but only on the one face 75 of the piston of FIG. 3. The device of FIG. 3 is of simpler mechanical construction of FIG. 2 in that the piston assembly communicates directly with one of the cavities 131 and no iiange, such as iiange 28 in FIG. 2, ils required in the piston assembly 20.

The transducer shown in FIG. 4 is similar to those Iof FIGS. 2 and 3 in that the valving is of the push-pull variety and also in that the acoustic tank circuit is identical. In the device of FIG. 4, as in the device of FIG. 3, mechanical springs 72 are used for compliance in the load clzoupling circuit, rather than the liuid iilled cavity 65 of The distinction between the device of FIG. 4 and the previous devices is that the push-pull amplifier now is coupled to a push-pull Aor `dipole radiating element 221 which comprises two rigidly interconnected portions 221A and 221B. The composite radiating element 221 moves as an integral piston driven in push-pull by the out-ofphase pressure variations in cavities 131 and .132 acting upon drive surfaces 75 and 76, respectively, of the composite radiating element 221. The central lstructure 77 which houses the electromechanical exciter 14, as well as the ow switch and the acoustic tank circuit, is now isolated from the external housing by a plurality of spring elements 72. When the portion 221A of piston radiator 221 undergoes a momentary motion to the right, the central structure 77 moves t-o the left `of its neutral position, and vi-ce versa.

FIG. illustrates a transducer which differs from those shown previously in that one of the fluid-filled cavities, namely, cavity 32, is blocked so that single-ended valving is obtained instead of push-pull switching. Except for this feature, the device of FIG. 5 is the same as that shown in FIG. 2. In the device of FIG. 5, the flow of fluid from cavity 31 only is ported -to valve 140 through port 52. The acoustic circuit of the transducer of FIG.. 5 remains the :same as that of FIG. 2, with the exception ofthe flow modulating source. The device of FIG. 5, like that of FIG. 2, uses a push-pull output coupling circuit, with the pressure variations within cavities 31 and 32 acting upon opposite faces of the piston drive fiange 28.

A fundamental distinction between the device of FIG. 5 and that of FIG. 2 is that the former device permits frequency dou-bling to be obtained by proper construction of the valve 140 relative to port structure 45. For example, as shown in FIG. 5, there is, at equilibrium, a symmetrical overlap of 70% of the valve metering rims 137 and 138 relative to the respective stator port metering rims 141 and 142. ,During a portion of the valving cycle when the valve 140 is driven to the left of its equilibrium position, fluid ows through orifice 134; on the other hand,

during some portion of the rightward excursion of valve d 140 from its equilibrium position, fluid fiows through open orifice 135. Since each of the orifices 134 and 13S open once during each valving cycle, the frequency tof flow modulation will be twice that of the input electrical control signal. In other words, if the peak displacement of the valving means is such that the orifices at opposite ends of the valving means connecting through a :common fluid cavity each :open once for each oscillation cycle of the valving means, the frequency of the acoustic energy at the amplifier output will be twice that of the input signal. If, on the other hand, the peak displacement of the valving mean-s is never great enough for one of the two orifices to open during the oscillation cycle of the valving means, the frequency of ioutput energy is equal to the frequency of the input signals. Frequency doubling can be accomplished only in those devices which, like that shown in FIG. 5, employ single-ended valving; other examples of such devices are those shown in FIGS. 6 and 7.

Although valving could be accomplished if the central land of valve 140, as shown in FIG. 5, were connected directly to the connecting rod 63 instead of being connected to the left-hand land of valve 140, practical considerationdictates that outer lands 'be disposed on opposite sides of a central land in order that there be no net static thrust exerted upon the central land by virtue of its exposure to the high pressure side Iof the fiuid path. With the three-land valves shown in FIG. 5, any force exerted on the oppositely disposed lands are in opposition and, consequently, no net thrust is exerted on the valve.

It should be noted that the same type operation as achieved by the device of FIG. 5 can be lobtained by overlapping the left-hand land of valve 40 yof FIG. 2 so that it never permits the left-hand port 53 of FIG. 2 to pass fluid. v

FIG. 6 discloses a device which differs essentially from that of FIG. 5 inthat the output coupling device is singleended. In this respect, the device of FIG. 6 is like that shown in FIG. 3. Since push-pull flow modulation is not accomplished in the device lof FIG. 6, the cavities or chambers 131 and 132 need not be symmetrical, as in the case of the device of FIG. 3. Since cavity 332 is shown larger than cavity 131 in FIG. 6, the zero pressure point (acoustic ground) along loop 650 will be nearer the larger {cavity 132. The feed line 47 then will connect to loop 650 at a point between the entrance to cavity 132 and the mid-point of loop 650.

FIG. 7 discloses a single-ended amplifier which, in-

' stead'of being coupled to a single-ended piston radiator as in FIG. 6, is coupled to a double-ended piston radiating assembly wherein the individual pistons 321 and 321 move in push-push. The device of FIG. 7 distinguishes from that of FIG. 4 in that the latter disclosed push-pull fiow modulation and in that the two portions 221A and 221B of FIG. 4 move as a unitary structure instead of independently, as in the case of the device of FIG. 7. It should be noted that the inertance line 150 in FIG. 7 is no longer a loop, as in the case of the inertance loops in FIGS. 2-6.

VWhereas the single-ended amplifier may be Somewhat easier to construct, the inclusion of push-pull amplification will improve the response of the transducer to nonsymmetrical waveform inputs and will increase its power handling capability by a factor of two for the same valve stroke.

The devices of FIGS. 2-7 have been illustrated, for the sake of simplicity, with a single stage valve amplifier. For high power devices, a multistage valve amplifier is generally required; such :a device is shown in FIG. S. It should be understood, however, that a multistage valve combination of the type shown in FIG. 8 may be incorporated into any of the devices previously described.

The housing 323 of FIG. 8 includes a web-like structure extending diametrically into the `large fluid-filled chamber 165 which serves as a backing compliance for the piston assembly 26.

The acoustic power output of the device of FIG. 8 is developed by virtue of the motion of the substantially rigid piston radiator 21 which is driven by push-pull pressures generated in drive cavities 31 and 32 by the twostage valve amplifier including pilot valve 240 and power valve 209. Hydraulic fluid at constant supply pressure is introduced at an inlet line 247 midway between the amplifier stages andthe fluid discharges to the reservoir through outlet lines 256a and 2561;. The amplifier is actuated by moving coil transducer 214 attached to the first, or pilot, valve stage 240. The exciter 214 may ininclude a pair of coils 258:1 and 25812 wound in opposite directions upon two spiders 263g and 26311 attached to opposite ends of pilot valve 240. An electrical input signal from a remote point outside the housing 323 provides excitation for the coils. It is obvious that only one coil may be used instead of the two shown in FIG. 8; however, the use of two magnet-coil assemblies may provide improved drive characteristics.

The valving stages 240 and 200 of FIG. 8 incorporate closed center, four-way spool valves. The .term closed center means that all orifices are substantially closed when the valve is in its center or null position. The term four-way refers to the fact that the circuit of the valve is such -that the flow resistance of the four orifices S2, S3, 84 and S5 of valve 240, and the four orifices 86, 87, 88 and S9 of valve 200, will vary simultaneously in response to motion of the spool valve. If the pilot spool valve 240 is displaced to the right, the flow resistance of orifices 83 and 8S will decrease while the resistance presented by orifices 82 and 84 will increase. Consequently, there is developed across the driving area 91 of power spool valve 20G a force unbalance tending to displace valve 200 to the right. This resulting displacement modifies the fiow resistance presented by the orifices 86, 87, 88 and 89 of the main ports and, in turn, allows a forced unbalance to develop across the area 94 of the drive flange 2S of piston 21, forcing the piston to move to the left.

If the pilot valve 240 moves to the left, on the other hand, the flow resistance of orifices 83 and S5 will increase while the resistance offered by orifices 82 and 84 will decrease. The resulting force developed across driving area 92 of valve 20) is such as to displace valve 280 to the left. Thus, a force is exerted on the surface 95 of drive fiange 28 of piston 21, causing the piston to move to the righ-t. The resulting motion of the piston conveys power to an external load.

Although the valving arrangements shown in FIG. 8 may appear similar to that of the conventional hydraulic servo valve, several differences should be noted. The

conventional electrohydraulic servo valve normally is used for position control and is an integrating device wherein the net volume of fluid passed by the valve is Ithe integral of the valves position history about a null or balanced ow point. In position control, the valving stages always operate in the vicinity of this null point and, since high sensitivity about this position is desired, extremely close tolerances and knife-edged metering orifices are required. In the case of acoustic power generation by the valving means shown in FIG. 8, the attainment of high signal power levels requires large valve stroking and the valve will pass the null position with maximum velocity. Consequently, clearances can be enlarged and Ithe orifices may be machined under less precise conditions. The complexity of conventional electrohydraulic servo Valves generally follows from the requirement for obtaining closed loop performance. Feedback of a mechanical or an electromechanical nature around one or more stages of an electrohydraulic amplifier is essential if absolute control over output position is to be maintained. From the standpoint of acoustic power generation, -the variational velocity of the output member (piston radiator) is of greater concern than its absolute position. Open loop performance is possible in the case of acoustic power generation provided simple and practical means are used Ito insure adequate stability of the piston and valving means; consequently, considerable simplification and increased reliability can be obtained. Whereas the electrohydraulic servo mechanism is essen# tially a direct current feedback amplifier in which force and position control down to zero frequency is required, the requirements in the case of acoustic power generation-particularly in the case of the amplifier according to the invention-are limited to alternating current power amplification over a rather limited bandwidth.

The response of the piston coupler in FIG. 8 to static flow, .as might develop between cavities 31 and 32 as a result of minor drifts in the `average position of the main spool valve 200, has been eliminated by the presence yof the loop 50 interconnecting the drive cavities. This loop presents a short circuit between the cavities at zero frequency, yet presents a finite impedance to alternating pressure differentials in the operating frequency range. The presence of loop 50 provides the stabilizing feature which, in conventional hydraulic systems, is accomplished by electromechanical or mechanical feedback loops. It is evident that the loop 50 limits the bandwidth of the system according to the invention, since, in addition to zero static response, the loop 50 presents a short circuit when its length is one wavelength in the contained uid. The effect of loop 50 th-us is to convert the system from a direct current amplifier to an alternating current amplifier of limited bandwidth.

The acoustic circuit of the device of FIG. 8 is similar to that shown in FIG. 2.

Single-ended and push-pull flow modulating means have been described heretofore which have been coupled interchangeably to single-ended, push-pull or pushpush coupling structures. In the case of push-pull flow modulation, as applied to single-ended coupling means as exemplified by the device of FIG. 3, the power conversion performance of such a system may be compromised when the acoustic tank circuit and the output coupling structure are designed for extremely broad bandwidth response. This results from the fact that the combination of cavities 131 and 132 and loop 50 in the device of FIG. 3, under heavily loaded conditions, does not enable acoustic energy developed in cavity 132 by the ow modulation through orifice 35 to be transferred through loop 50 in such phase as to aid effectively the energy developed in cavity 131 by the flow modulation through orifice 34, in driving the output coupling assembly 120. In order to achieve the push-pull flow modulation with single-ended coupling under relatively broadband conditions, it may be desir- 'l0 able to have the push-pull modulation occur at the cavity which is contiguous with the output coupling means 120. Such an arrangement is shown in FIG. 9.

By means of the arrangement of FIG. 9, push-pull` modulation can be associated vsnth the cavity 131` contiguous with the piston coupler during the entire input signal cycle rather than having to depend for half of the input signal cycle upon energy being introduced from the back cavity 132 by way of loop 50 into the active cavity 1311 in the proper phase to aid excitation of the piston 121, as in the device of FIG. 3.

In the device of FIG. 9, one or the other of orifices 334 or 335 is always open to modify the pressure in cavity 131 in accordance with the input signal. If, for example, valve 300 moves to the left, the supply orifice 334 opens, fluid passes therethrough from supply line 437 and the pressure in drive cavity 131 approaches the supply pressure. On the other hand, a movement of the valve to the right ca-uses orifice 335 to open thereby permitting fluid to pass therethrough to the loW pressure side of the fluid pump by way of return line 456; the pressure in cavity 131 then moves toward the return pressure.

The devices of FIGS. 3 and 9 are able to respond to non-periodical input signals, whereas a device su-ch as shown in FIG. 6 which incorporates both single-ended modulation as well as single-ended coupling means, may cause distortion of the input signals, in certain broadband applications, during a portion of the input cycle.

FIG. 10 illustrates a transducer having a two-stage valve and involving a technique for establishing and maintaining the equilibrium position of the power stage valve, such as valve 200 of FIG. 8, without requiring mechanical elements, such as springs, which would fail under repeated stroking of the valve. Although the technique shown in FIG. 9 may be used with the four- Way spo-ol Valves 240 and 200 of FIG. 8, the pilot valve 440 of FIG. 10 is of the type shown in FIG. 5 while the power valve 300 of FIG. 10` is of the type shown in FIGS. 2-4.

In the absence of any centering mechanism, a slight unbalance in the null position of the pilot valve 440 of FIG. 10 would result in an unbalance of forces on the end faces or rims 301 yand 302 of power valve 300, thereby causing it to drift in one direction or the other. A stable null position of valve 300 is obtained by the action of variable area orifices 303 and 304 dened by the end rims 301 and 302 of valve 300 and the corresponding ribs 307 and 308 of grooves 305 and 306. Normally, the average pressure in cavities 391 and 392 at the ends of the power spool is aibout midway between the supply and return pressure, as determined by the pressure drop across orifices 402, 403, 404 and 405 of the four-way pilot valve 440. If the average pressures in the cavities 391 and 392 are unequal, the power valve 300 obviously will drift. If, for example, the power valve 300 tends to drift to the left, orifice 303 will tend to open and orifice 304 will tend to close. Since orifice 303 returns to the low pressure side of the hydraulic system through line 395 and output connections 356a, the more orifice 303 opens the greater will become the fiow through that orifice, the greater will become the press-ure drop across supply orifice 402 because of its interposition in the flow path, and the lower will be the pressure in cavity 391. On the other hand, the flow will be reduced at the left orifice 304 of power valve 300. This reduction in flow will be accompanied by a reduction in the pressure drop across the left supply orifice 403 of the pilot valve 440, and will result in an increase of pressure in cavity 392. In other words, a drift to the left of power valve 300- is accompanied by an increase in pressure in the lefthand cavity 392 and a reduction in pressure in cavity 391, tending to force the valve 300 back to the right. The inuence of the shunting orifices 303 and 304 is to provide a high gain feedback amplifier to stabilize the equilibrium position of power valve 300 so that its outer faces 301 and 302 are substantially at zero lap condition with respect to the outer rims 307 and 303 of grooves 305 and 306, all respectively, provided that the pilot valve 440 is in proper adjustment. The null position of pilot Valve 440 may be adjusted either mechanically, as by adjusting the length of connecting rod 63 which is threaded at one end and passes through a bushing attached to spider 62 and a nut 67, or by variation of a direct current bias voltage supplied to the exciter coil 58.

Lines 395 and 396 on the low pressure side of orifices 303 and 304 are intended to be long enough and of sufficiently small diameter so that over the frequency range that the valve stages may be driven they exhibit an acoustic impedance that is large compared with the mass reactance of the valve 300. Thus, Whereas orifices 303 and 304 can act to center the power valve 300 on a static basis, they are prohibited from infiuencing its dynamic behavior because the flow through the orifices 303 and 304 cannot vary appreciably over the period of valve motion owing to the high terminal reactance.

It is evident that for orifices 303 and 304 to be effective in centering valve 300, it must tbe possible for the static pressures to equalize in cavities 391 and 392 at some position of valve 300 within the effective control range of orifices 303 and 304. If, for example, pilot stage valve 440 is assumed to be out of null adjustment, and orifice 403 is closed such that the pressure in cavi-ty 392 is essentially zero, then the centering capabilities of the two orifices 303 and 304 are hivhly, if not entirely, compromised. In order to avoid the above effect, supply orifices 402 and 403 of pilot valve can be slightly underlapped, so `that variations in the null position of the pilot valve will not close off the flow through one side. In addition, therefore, it is desirable to supply fluid independently and directly to cavities 391 and 392, and hence to power valve centering orifices 303 and 304, through separate 'adjustable flow resistances, such as valves 9S and 99, and supply lines 347 and 347" of high acoustic impedance. In

other words, inlet line 347 of FIG. 10 may be supplemented by two separate lines 347 and 347, each passing through the housing and communicating with a different one of cavities 391 and 392. The adjustable resistances 98 and 99 then are essentially in parallel with respective pilot valve supply orifices 402 and 403 and can, therefore, be employed to establish the desired equilibrium position of the power stage valve 300, essentially independently of the equilibrium position of the pilot valve. Again, the high reactance lines 347 and 347" would isolate the static positioning circuit from the dynamic circuit ofthe two stage valve assembly.

What is claimed is:

I. A hydroacoustic device comprising (a) a housing having a cavity therein,

(b) a valving member disposed in said cavity, moveable about a center position,

(c) means including a first path in said housing for passing fluid under pressure through said cavity under the control of said valving member for establishing acoustic vibrations,

(d) said valving member and the walls of said cavity defining at least one chamber,

(e) impedance means in a second path in said housing communicating with said chamber for the flow of fiuid into and out of said chamber,

() said impedance means including a fiuid line having an acoustic impedance higher than that of said valving member at the frequency of vibration of said valving member, and

(g) said valving member and said walls of said cavity defining at least one orifice for controlling the flow of fiuid to said one chamber so that motion of said Valving member with respect to said center position at a frequency lower than the frequency of said acoustic vibrations results in a pressure variation in said chamber, which pressure variation urges said valving member to said center position.

2. The invention as set forth in claim 1, wherein said housing has another cavity, a slidable member partially disposed in said other cavity, said valve cavity being coupled to said other cavity for transferring said acoustic vibrations thereto, said other cavity and said slidable member comprising a load coupling means.

3. A hydroacoustic device comprising (a) a housing having a cavity therein,

(b) a valving member disposed in said cavity moveable about a center position,

(c) means including a first path in said housing for passing fluid under pressure through said cavity under the control of said valving member for establishing acoustic vibrations,

(d) said valving member and the walls -of said cavity defining first and second chambers,

(e) said valving member having first and second opposite faces respectively exposed in said first and second chambers,

(f) impedance means in a second path in said housing communicating with said first and second chambers for the alternate fiow of fiuid into and out of said first and se-cond chambers,

(g) said impedance means including first and second fiuid lines, each having an acoustic impedance higher than that of said valving member at the frequency of vibration of said valving member, and

(h) said valving member and said walls of said cavity defining first 'and second orifices coacting with said impedance means for controlling the fiow of fiuid to said first and second chambers, so that motion of said valving member with respect to said Icenter position at a frequency lower than the frequency of said acoustic vibrations results in pressure variations in said first and second chambers, which pressure variations urge said valving member to said center position.

4. An acoustic vibration transducer for operation over a certain frequency range comprising (a) a housing having a primary path for the flow therethrough of fluid under pressure,

(b) said housing having a cavi-ty in said primary path,

(c) a free-floating valve member slidably disposed in said cavity and defining a pair of chambers independent of said primary path in said cavity and on opposite sides of said valve member,

(d) said valve member having a `certain acoustic impedance over said range,

(e) condui-t means communicating separately with different ones of said pair of chambers for the flow of fluid through said pair of chambers,

(f) said valve member and the walls of said pair of chambers defining separate orifices in said secondary path for controlling the flow of fluid through said different ones of said pair of chambers,

(g) said conduit means presenting an acoustic impedance higher than that of said valve member at the frequency of vibration of said valve member, and

(h) means including said valve member for deriving acoustic energy from the fiow of energy of said fiuid in said primary path when said valve member is vibrated about a center position, and

(i) said conduit means, said pair of chambers, said valve member, and said separate orifices coacting so that motion of said valve member with respect to said given center position at a rate lower than the rate of said vibrations establishes a differential pressure in said pair of chambers for restoring said valve member to said center position.

5. The invention as set forth in claim 4, wherein said housing has another cavity, a piston member movably disposed in said other cavity and defining a second pair of chambers therein, said valve cavity being coupled to said 13 second pair of chambers for transferring said acoustic vibration energy thereto, a loop conduit, the opposite ends of said conduit being respectively coupled to diierent ones of said second pair of chambers, said second pair of chambers and said piston member comprising a load coupling means.

6. The invention as set forth in claim wherein said loop has a length less than one wavelength at the uppermost frequency in said range.

7. An `acoustic; vibration transducer for generating acoustic vibration over a certain frequency range, said transducer comprising:

(a) a housing having a cavity therein,

(b) a valve movable Within said cavity, the opposite ends of said valve and the end walls of said cavity dening a pair of chambers,

(c) said valve having a certain acoustic impedance over said range,

(d) orifices deiined by the walls of different ones said chambers and said valve,

(e) a first conduit including a rst chamber communicating with one of said pair of chambers through one of said orifices, said rst conduit having an impedance which is large compared to said valve impedance,

(f) a second conduit also having said large impedance communicating with the other one of said pair of chambers through the other one of said orifices,

(g) means for passing uid under pressure between said ports, and

(h) means including said valve for transducing fluid ow energy into acoustic vibrations over said range.

8. A two stage valving device comprising (a) a rst stage including a rst valving member for controlling the flow of uid under pressure to at least two diierent lines from a source of fluid pressure when said valving member is vibrated,

(b) means connected to said rst stage for selectively vibrating said rst valving member over a given range of frequencies in response to an external signal,

(c) a second stage including a housing,

(d) a cavity in said housing,

(e) a free oating valving member slideably disposed 14 in said `cavity whereby said free oating valving member separates said cavity into first and second chambers each connected to `a different one of said different lines,

(f) said valving member having a certain acoustic irnpedance over said frequency range,

(g) irst and second porting structures each including one end of said free floating valve for varying the ow of fluid from each of said rst and second chambers,

(h) first and second conduit means connected to said first and second porting structures respectively,

(i) said conduit means having an acoustic impedance that is high compared to said acoustic impedance of said valving member over said frequency range, and

(j) said valving member, porting structure and conduit means -coacting so that motion of said free floating valving member with respect to said porting structure at a frequency substantially lower than said given range of frequencies, results in an average differential pressure in said rst and second chambers, which diierential pressure urges said free oating valving member to a given average center position during said vibrations.

9. The invention defined in claim 8 further including rst and second fluid pressure supply lines connected to said rst and second chambers and said source of uid pressure and means for adjusting ythe fluid pressure in each of said fluid pressure supply lines to establish said center position of said valving member.

References Cited by the Examiner UNITED STATES PATENTS 3,004,512 10/1961 Bouyoucos 116-137 FOREIGN PATENTS 567,557 11/1958 Belgium.

BENJAMIN A. BORCHELT, Primary Examiner.

P. A. SHANLEY, Assistant Examiner. 

1. A HYDROACOUSTIC DEVICE COMPRISING (A) A HOUSING HAVING A CAVITY THEREIN, (B) A VALVING MEMBER DISPOSED IN SAID CAVITY, MOVEABLE ABOUT A CENTER POSITION, (C) MEANS INCLUDING A FIRST PATH IN SAID HOUSING FOR PASSING FLUID UNDER PRESSURE THROUGH SAID CAVITY UNDER THE CONTROL OF SAID VALVING MEMBER FOR ESTABLISHING ACOUSTIC VIBRATIONS, (D) SAID VALVING MEMBER AND THE WALLS OF SAID CAVITY DEFINING AT LEAST ONE CHAMBER, (E) IMPEDANCE MEANS IN A SECOND PATH IN SAID HOUSING COMMUNICATING WITH SAID CHAMBER FOR THE FLOW OF FLUID INTO AND OUT OF SAID CHAMBER, (F) SAID IMPEDANCE MEANS INCLUDING A FLUID LINE HAVING AN ACOUSTIC IMPEDANCE HIGHER THAN THAT OF SAID VALVING MEMBER AT THE FREQUENCY OF VIBRATION OF SAID VALVING MEMBER, AND (G) SAID VALVING MEMBER AND SAID WALLS OF SAID CAVITY DEFINING AT LEAST ONE ORIFICE FOR CONTROLLING THE FLOW OF FLUID TO SAID ONE CHAMBER SO THAT MOTION OF SAID VALVING MEMBER WITH RESPECT TO SAID CENTER POSITION AT A FREQUENCY LOWER THAN THE FREQUENCY OF SAID ACOUSTIC VIBRATIONS RESULTS IN A PRESSURE VARIATION IN SAID CHAMBER, WHICH PRESSURE VARIATION URGES SAID VALVING MEMBER TO SAID CENTER POSITION. 